plus-one.js

/**
 * @param {number[]} digits
 * @return {number[]}
 */
var plusOne = function (digits) {
  const n = digits.length;
  for (let i = n - 1; i >= 0; i--) {
    if (digits[i] < 9) {
      digits[i]++;
      return digits;
    } else {
      digits[i] = 0;
    }
  }
  // If all digits are 9, we need to add one more digit
  return [1, ...digits];
};